High voltage monolithic LED chip with improved reliability

ABSTRACT

Monolithic LED chips are disclosed comprising a plurality of active regions on a submount, wherein the submount comprises integral electrically conductive interconnect elements in electrical contact with the active regions and electrically connecting at least some of the active regions in series. The submount also comprises an integral insulator element electrically insulating at least some of the interconnect elements and active regions from other elements of the submount. The active regions are mounted in close proximity to one another to minimize the visibility of the space during operation. The LED chips can also comprise layers structures and compositions that avow improved reliability under high current operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/944,356 filed on Jul. 31, 2020, and subsequently issued as U.S. Pat.No. 11,588,083, which is a continuation of U.S. patent application Ser.No. 16/290,084 filed on Mar. 1, 2019 and subsequently issued as U.S.Pat. No. 10,957,830, which is a continuation of U.S. patent applicationSer. No. 14/699,302 filed on Apr. 29, 2015 and subsequently issued asU.S. Pat. No. 10,243,121, which is a continuation-in-part of U.S. patentapplication Ser. No. 14/050,001 filed on Oct. 9, 2013 and subsequentlyissued as U.S. Pat. No. 9,728,676, which is a continuation-in-part ofU.S. patent application Ser. No. 13/168,689 filed on Jun. 24, 2011 andsubsequently issued as U.S. Pat. No. 8,686,429, wherein the entiredisclosures of the foregoing applications and patents are herebyincorporated by reference herein.

FIELD OF THE DISCLOSURE

This invention relates to monolithic light emitting diode (LED) chips,and in particular to high voltage monolithic LED chips with multipleactive regions arranged in series and in close proximity.

BACKGROUND

Light emitting diodes (LED or LEDs) are solid state devices that convertelectric energy to light, and generally comprise one or more activelayers of semiconductor material sandwiched between oppositely dopedlayers. When a bias is applied across the doped layers, holes andelectrons are injected into the active layer where they recombine togenerate light. Light is emitted from the active layer and from allsurfaces of the LED.

For typical LEDs it is desirable to operate at the highest lightemission efficiency, and one way emission efficiency can be measured isby the emission intensity in relation to the input power, or lumens perwatt. One way to maximize emission efficiency is by maximizingextraction of light emitted by the active region of LEDs. Forconventional LEDs with a single out-coupling surface, the externalquantum efficiency can be limited by total internal reflection (TIR) oflight from the LED's emission region. TIR can be caused by the largedifference in the refractive index between the LED's semiconductor andsurrounding ambient. Some LEDs have relatively low light extractionefficiencies because of the high index of refraction of the substratecompared to the index of refraction for the surrounding material (e.g.epoxy). This difference results in a small escape cone from which lightrays from the active area can transmit from the substrate into the epoxyand ultimately escape from the LED package. Light that does not escapecan be absorbed in the semiconductor material or at surfaces thatreflect the light.

Different approaches have been developed to reduce TIR and improveoverall light extraction, with one of the more popular being surfacetexturing. Surface texturing increases the light escape probability byproviding a varying surface that allows photons multiple opportunitiesto find an escape cone. Light that does not find an escape conecontinues to experience TIR, and reflects off the textured surface atdifferent angles until it finds an escape cone. The benefits of surfacetexturing have been discussed in several articles, [See Windisch et al.,Impact of Texture-Enhanced Transmission on High-Efficiency SurfaceTextured Light Emitting Diodes, Appl. Phys. Lett., Vol. 79, No. 15,October 2001, Pgs. 2316-2317; Schnitzer et al. 30% External QuantumEfficiency From Surface Textured, Thin Film Light Emitting Diodes, Appl.Phys. Lett., Vol 64, No. 16, October 1993, Pgs. 2174-2176; Windisch etal. Light Extraction Mechanisms in High-Efficiency Surface TexturedLight Emitting Diodes, IEEE Journal on Selected Topics in QuantumElectronics, Vol. 8, No. 2, March/April 2002, Pgs. 248-255; Streubel etal. High Brightness AlGaNInP Light Emitting Diodes, IEEE Journal onSelected Topics in Quantum Electronics, Vol. 8, No. March/April 2002].Additionally, U.S. Pat. No. 6,657,236, also assigned to Cree Inc.,discloses structures formed on the semiconductor layers for enhancinglight extraction in LEDs.

Another way to increase light extraction efficiency is to providereflective surfaces that reflect light so that it contributes to usefulemission from the LED chip or LED package. In a typical LED package 10illustrated in FIG. 1 , a single LED chip 12 is mounted on a reflectivecup 13 by means of a solder bond or conductive epoxy. One or more wirebonds 11 connect the ohmic contacts of the LED chip 12 to leads 15Aand/or 15B, which may be attached to or integral with the reflective cup13. The reflective cup may be filled with an encapsulant material 16which may contain a wavelength conversion material such as a phosphor.Light emitted by the LED at a first wavelength may be absorbed by thephosphor, which may responsively emit light at a second wavelength. Theentire assembly is then encapsulated in a clear protective resin 14,which may be molded in the shape of a lens to collimate the lightemitted from the LED chip 12. While the reflective cup 13 may directlight in an upward direction, optical losses may occur when the light isreflected. Some light may be absorbed by the reflector cup due to theless than 100% reflectivity of practical reflector surfaces. Some metalscan have less than 95% reflectivity in the wavelength range of interest.

FIG. 2 shows another conventional LED package 20 that may be more suitedfor high power operations that can generate more heat. In the LEDpackage 20, one or more LED chips 22 are mounted onto a carrier such asa printed circuit board (PCB) carrier, substrate or submount 23. Areflector 24 can be included on the submount 23 that surrounds the LEDchip(s) 22 and reflects light emitted by the LED chips 22 away from thepackage 20. Different reflectors can be used such as metal reflectors,omni-directional reflectors (ODRs), and distributed Bragg reflectors(DBRs). The reflector 24 can also provide mechanical protection to theLED chips 22. One or more wirebond connections 11 are made between ohmiccontacts on the LED chips 22 and electrical traces 25A, 25B on thesubmount 23. The mounted LED chips 22 are then covered with anencapsulant 26, which may provide environmental and mechanicalprotection to the chips while also acting as a lens. The metal reflector24 is typically attached to the carrier by means of a solder or epoxybond.

The reflectors shown in FIGS. 1 and 2 are arranged to reflect light thatescapes from the LED. LEDs have also been developed having internalreflective surfaces to reflect light internal to the LEDs. FIG. 3 showsa schematic of an LED chip 30 with an LED 32 mounted on a submount 34 bya metal bond layer 36. The LED further comprises a p-contact/reflector38 between the LED 32 and the metal bond 36, with the reflector 38typically comprising a metal such as silver (Ag). This arrangement isutilized in commercially available LEDs such as those from Cree® Inc.,available under the EZBright™ family of LEDs. The reflector 38 canreflect light emitted from the LED chip toward the submount back towardthe LED's primary emitting surface. The reflector also reflects TIRlight back toward the LED's primary emitting surface. Like the metalreflectors above, reflector 38 reflects less than 100% of light and insome cases less than 95%. The reflectivity of a metal film on asemiconductor layer may be calculated from the materials' opticalconstants using thin film design software such as TFCalc™ from SoftwareSpectra, Inc. (www.sspectra.com). U.S. Pat. No. 7,915,629, also assignedto Cree Inc. and fully incorporated herein by reference, furtherdiscloses a higher efficiency LED having a composite high reflectivitylayer integral to the LED for improving emission efficiency.

In LED chips having a mirror contact to enhance reflectivity (e.g. U.S.Patent Publication No. 2009/0283787, which is incorporated in itsentirety herein by reference), the light extraction and external quantumefficiency (EQE) is strongly affected by the reflectivity of the mirror.For example, in a mirror comprised of Ni/Ag, the reflectivity isdominated by the properties of the Ag, which is >90% reflective.However, as shown in FIG. 4 , such a mirror 40 is traditionally borderedby a metal barrier layer 42 that encompasses the edges of the mirror,with the barrier layer 42 provided to prevent Ag migration duringoperation. The metal barrier layer 42 has much lower reflectivity thanthe mirror (e.g. 50% or lower), and the portions of the barrier layer 42contacting the active layer 44 outside the mirror 40 periphery can havea negative effect on the overall efficiency of the LED chip. This isbecause such portions of the metal barrier layer 42 absorb many of thephotons that would otherwise exit the chip. FIG. 5 depicts another LEDchip 50 in the EZ family of Cree, Inc. lights, with the chip 50comprising a mirror 52 disposed below an active region 54. As in FIG. 4, a barrier layer 56 is provided that borders mirror 52 as well asextending outside the periphery of the mirror. Those portions of themetal barrier layer extending beyond the edges of the mirror 52 canlikewise absorb some of the light emitted from the LED(s) and impact theoverall emitting efficiency of the chip.

In LED chips comprising a plurality of junctions or sub-LEDs, such asthose disclosed in U.S. Pat. No. 7,985,970, and U.S. Patent Pub. No.2010/0252840 (both assigned to Cree Inc. and incorporated entirelyherein by reference), the effect of the metal barrier layer can beparticularly pronounced. FIG. 6 depicts a monolithic LED chip comprisinga plurality of sub-LEDs and a plurality of contact vias 62. Portions ofbarrier layers 64, as represented by the dark circles at the peripheriesof the vias 62, are exposed and illustrate the dimming effect that canresult from such exposure of the barrier layer. The effect can be verypronounced when comparing the efficiency of large, single-junction chipsto multi-junction chips of the same footprint. This is because thesmaller the junction is relative to the barrier layer exposed at themirror periphery, the more severe the impact is on the overall emissionefficiency of the device. For example, a 16-junction, 1.4 mm LED chipcan be approximately 10% dimmer than a single-junction 1.4 mm chip.

SUMMARY

Embodiments of the present invention are generally related to monolithicLED chips having a plurality of active areas on a substrate/submount(“submount”) that can be interconnected in series. It is understood thatother embodiments can have active regions interconnected in parallel orin a series parallel combination. The active areas can be arranged inclose proximity such that space between adjacent ones of the activeareas is substantially not visible when the emitter is emitting, therebyallowing the LED chip to emit light similar to that of a filament.Overall emission of the LEDs can also be improved by reducing thelight-absorbing effects of materials, such as barrier layers, adjacentto the mirror(s). Some embodiments are described below as having activeregions arranged linearly, but it is understood that the LED chipsaccording to the present invention can be arranged in many differentshapes with their active regions arranged in many different locationsand patterns in relation to one another. Some of the different shapesinclude different polygon shapes like triangle, square, rectangle,pentagon, etc.

Some embodiments of the present invention can be arranged to provide forimproved reliability under high power or high current operation. Some ofthese embodiments can have layer structures or composition that helpminimize or eliminate electromigration during high power LED chipoperation. Some embodiments of a monolithic LED chip, according to thepresent invention comprises a plurality of active regions, with anelectrically conductive interconnect element connecting at least two ofthe active regions. The interconnect element can comprise a materialand/or structure that resists electromigration.

An additional embodiment of the present invention allows for improvedreliability under high power density or high current density operation.For some embodiments of a monolithic chip it is advantageous to reducethe dimensions of the electrically conductive connection elements toimprove the overall emission of the LED chip. High power density and/orhigh current density in these electrically conductive layers can induceelectromigration and subsequent reduced performance or failure of theLED chip.

Some embodiments of LED chips according to the present invention cancomprise a plurality of active regions on a submount. Interconnectionlayers may be included in the submount that carry electrical signal toand are in electrical contact with the active regions. A reflectivelayer may be included between the submount and active regions that ispositioned to reflect LED chip light that would otherwise reach theinterconnection layers.

Other embodiments of LED chips according to the present invention cancomprise a plurality of active regions on a submount. Electricallyconductive interconnect elements are included in said submount, whereinthe interconnect elements are in electrical contact with the activeregions. The conductive interconnect elements comprise a first layer ofelectrically conductive material and a second layers of material havinga higher resistance to electromigration than said first layer.

Still other embodiments of LED chips according to the present inventioncomprise a plurality of active regions on a submount. Integralelectrically conductive interconnect elements are included in thesubmount, wherein the interconnect elements are in electrical contactwith said active regions. The conductive interconnect elements comprisea metal alloy interconnection layer.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description and the accompanyingdrawings which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a prior art LED package;

FIG. 2 is a sectional view of another prior art LED package;

FIG. 3 a sectional view of another embodiment of a prior art LED chip;

FIG. 4 is a sectional view of a prior art LED chip according to thepresent invention;

FIG. 5 is a sectional view of a prior art LED chip according to thepresent invention;

FIG. 6 is a top view of a prior art monolithic LED chip according to thepresent invention;

FIG. 7 is a sectional view of one embodiment of an LED chip according tothe present invention;

FIG. 8 is a sectional view of another embodiment of an LED chipaccording to the present invention;

FIG. 9 is a sectional view of another embodiment of an LED chipaccording to the present invention;

FIG. 10 is a top view of a monolithic LED chip according to the presentinvention;

FIG. 11 is a sectional view of another embodiment of an LED chipaccording to the present invention;

FIG. 12 is a sectional view of another embodiment of an LED chipaccording to the present invention.

FIG. 13 is a top view of one embodiment of an LED chip according to thepresent invention;

FIG. 14 is a top view of another embodiment of an LED chip according tothe present invention;

FIG. 15 is a top view of still another embodiment of an LED chipaccording to the present invention;

FIG. 16 is a sectional view of one embodiment of a monolithic LED chipaccording to the present invention;

FIG. 17 is a sectional view of the LED chip shown in FIG. 16 at anintermediate manufacturing step;

FIG. 18 is a sectional view of another LED chip according to the presentinvention at an intermediate manufacturing step;

FIG. 19 is another sectional view of the LED chip shown in FIG. 18 ;

FIG. 20 is a sectional view of another embodiment of a monolithic LEDchip according to the present invention;

FIG. 21 is a sectional view of the LED chip in FIG. 20 showing flow ofan electrical signal;

FIG. 22 is a sectional view of another embodiment of a monolithic LEDchip according to the present invention;

FIG. 23 is a sectional view of the LED chip in FIG. 22 showing flow ofan electrical signal;

FIG. 24 is a plan view of a monolithic emitter according to the presentinvention;

FIG. 25 is a front view of one embodiment of a car headlight accordingto the present invention.

FIG. 26 is a sectional view of another embodiment of a monolithic LEDchip according to the present invention;

FIG. 27 is a sectional view of the LED chip in FIG. 26 showing flow ofan electrical signal;

FIG. 28 is a top view of another embodiment of a monolithic LED chipaccording to the present invention showing flow of an electrical signal;and

FIG. 29 is a sectional view of one embodiment of an interconnectionmetal layer according to the present invention.

DETAILED DESCRIPTION

The present invention is described herein with reference to certainembodiments, but it is understood that the invention can be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein.

In some embodiments according to the present invention, LED chipstructures are provided to enhance the overall emission characteristicsof LEDs. The emission characteristics of LED chip structures havingmirror reflectivity are generally enhanced by limiting the amount ofdark or substantially non-reflective barrier material around theperiphery of highly reflective mirror components. In LED chips havingp-contacts with integral mirrors rather than ITO (such as in the EZfamily of chips provided by Cree, Inc.), the light extraction and EQE isstrongly affected by the reflective characteristics of the mirror. Forexample, in a mirror comprised of Ni/Ag, the reflectivity is dominatedby the properties of the Ag and is believed to be around 90% reflective.This high reflectivity can be counteracted by a barrier layer, which isused to prevent Ag migration during operation of the LED chip at hightemperatures and/or in humid conditions. The barrier layer, if allowedto extend substantially beyond the periphery of the mirror, cansignificantly adversely affect the reflectivity of the mirror since itgenerally has a reflectivity of 50% or lower and can absorb many of thephotons that would otherwise be exiting and emitting from the chip.

Thus, in certain embodiments of LED chip structures according to thepresent invention, barrier layers are provided that are patternedsmaller than the mirror layers they are protecting. As such, the barrierlayers are preferably no longer wrapping around the edges of the mirror,and thus are not exposed to light trapped within the GaN active region.In still other embodiments, there can be multiple sub-LEDs connected viajunctions to comprise one LED chip. In such structures, there willnecessarily be a small portion of the barrier layer that is exposedoutside a portion of the mirror periphery in order to create aconnection between the p-contact of one LED and the n-contact of anadjacent LED. In such embodiments, the amount of the barrier that isexposed is minimized such that at least 40% of the mirror periphery isfree from the barrier layer and its associated adverse effects. In otherembodiments, at least 50% of the mirror periphery is free from thebarrier layer, while in other embodiments at least 60% is free from thebarrier layer.

In other embodiments, LED chips structures are provided having aplurality of active areas/portions/regions (“regions”) that can beprovided on a submount having internal and integral electricalinterconnects to connect the LEDs in different series connections. Indifferent embodiments, the active regions can be distinct from eachother, with each having its own set of oppositely doped layers andactive layer not otherwise connected to same layers in the other activeregions.

The submount can also have a barrier layer that does not extend beyondthe edge of or wrap around the portions of the mirror layer, with theportion being particularly below the primary emission area of the activeregions. This can help minimize the light that might be absorbed duringoperation, thereby increasing the overall emission efficiency of theactive regions.

The internal electrical connections of the submount can be particularlyarranged to allow for interconnection of the active regions so that eachis relatively close to the adjacent ones of the active regions. Duringemission of the monolithic LED chips according to the present invention,the small space between the active regions reduces or eliminates darkspots between the active regions so that the LEDs appear as a continuouslight source. This arrangement allows for monolithic LEDs that give theappearance of a conventional filament light source, while at the sametime maximizing the emission area of the LED chips to increase overallbrightness.

Some embodiments of LED chips according to the present invention have aplurality of active areas regions on a submount and buried electricalinterconnects that can present certain reliability problems,particularly under high power operation. For example, in some of theseembodiments the buried electrical interconnects can experienceelectromigration of certain layers or materials during operation, whichcan lead to degradation and eventual failure of the device. One layerthat can experience electromigration is the buried electricalinterconnect. To address this, some embodiments of the present inventioncan be arranged to reduce, minimize or eliminate this electromigration.Some embodiments can have a layer structure that allow for the use ofmaterials for the current carrying layer that resist electromigration.Still other embodiments can have current carrying layers made ofmultiple layers with the outermost of the layers having lower tendencyto electromigrate. Still other embodiments provide layers as an alloy ofmaterials that also helps minimize electromigration.

It will be understood that when an element is referred to as being “on”,“connected to”, “coupled to”, or “in contact with” another element, itcan be directly on, connected or couple to, or in contact with the otherelement or intervening elements may be present. In contrast, when anelement is referred to as being “directly on”, “directly connected to”,“directly coupled to”, or “directly in contact with” another element,there are no intervening elements present. Likewise, when a firstelement is referred to as being “in electrical contact with” or“electrically coupled to” a second element, there is an electrical paththat permits current flow between the first element and the secondelement. The electrical path may include capacitors, coupled inductors,and/or other elements that permit current flow even without directcontact between conductive elements.

Although the terms first, second, etc. may be used herein to describevarious elements, components, regions, and/or sections, these elements,components, regions, and/or sections should not be limited by theseterms. These terms are only used to distinguish one element, component,region, or section from another element, component, region, or section.Thus, a first element, component, region, or section discussed belowcould be termed a second element, component, regions, or section withoutdeparting from the teachings of the present invention.

Embodiments of the invention are described herein with reference tocross-sectional view illustrations that are schematic illustrations ofembodiments of the invention. As such, the actual thickness ofcomponents can be different, and variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances are expected. Embodiments of the invention should notbe construed as limited to the particular shapes of the regionsillustrated herein but are to include deviations in shapes that result,for example, from manufacturing. A region illustrated or described assquare or rectangular will typically have rounded or curved features dueto normal manufacturing tolerances. Thus, the regions illustrated in thefigures are schematic in nature and their shapes are not intended toillustrate the precise shape of a region of a device and are notintended to limit the scope of the invention.

It is also understood that when an element such as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. Furthermore, relative terms such as “inner”, “outer”, “upper”,“above”, “lower”, “beneath”, and “below”, and similar terms, may be usedherein to describe a relationship of one layer or another region. It isunderstood that these terms are intended to encompass differentorientations of the device in addition to the orientation depicted inthe figures.

LED structures, features, and their fabrication and operation aregenerally known in the art and only briefly discussed herein. LEDs canhave many different semiconductor layers arranged in different ways andcan emit different colors. The layers of the LEDs can be fabricatedusing known processes, with a suitable process being fabrication usingmetal organic chemical vapor deposition (MOCVD). The layers of the LEDchips generally comprise an active layer/region sandwiched between firstand second oppositely doped epitaxial layers, all of which are formedsuccessively on a growth substrate or wafer. LED chips formed on a wafercan be singulated and used in different application, such as mounting ina package. It is understood that the growth substrate/wafer can remainas part of the final singulated LED or the growth substrate can be fullyor partially removed.

It is also understood that additional layers and elements can also beincluded in the LEDs, including but not limited to buffer, nucleation,contact and current spreading layers as well as light extraction layersand elements. The active region can comprise single quantum well (SQW),multiple quantum well (MQW), double heterostructure or super latticestructures.

The active region and doped layers may be fabricated from differentmaterial systems, with one such system being Group-III nitride basedmaterial systems. Group-III nitrides refer to those semiconductorcompounds formed between nitrogen and the elements in the Group III ofthe periodic table, usually aluminum (Al), gallium (Ga), and indium(In). The term also refers to ternary and quaternary compounds such asaluminum gallium nitride (AlGaN) and aluminum indium gallium nitride(AlInGaN). In a possible embodiment, the doped layers are galliumnitride (GaN) and the active region is InGaN. In alternative embodimentsthe doped layers may be AlGaN, aluminum gallium arsenide (AlGaAs) oraluminum gallium indium arsenide phosphide (AlGalnAsP) or aluminumindium gallium phosphide (AlInGaP) or zinc oxide (ZnO).

The growth substrate/wafer can be made of many materials such assilicon, glass, sapphire, silicon carbide, aluminum nitride (AIN),gallium nitride (GaN), with a suitable substrate being a 4H polytype ofsilicon carbide, although other silicon carbide polytypes can also beused including 3C, 6H and 15R polytypes. Silicon carbide has certainadvantages, such as a closer crystal lattice match to Group III nitridesthan sapphire and results in Group III nitride films of higher quality.Silicon carbide also has a very high thermal conductivity so that thetotal output power of Group-III nitride devices on silicon carbide isnot limited by the thermal dissipation of the substrate (as may be thecase with some devices formed on sapphire). SiC substrates are availablefrom Cree Research, Inc., of Durham, North Carolina and methods forproducing them are set forth in the scientific literature as well as ina U.S. Pat. Nos. Re. 34,861; 4,946,547; and 5,200,022.

LEDs can also comprise additional features such as conductive currentspreading structures, current spreading layers, and wire bond pads, allof which can be made of known materials deposited using known methods.Some or all of the LEDs can be coated with one or more phosphors, withthe phosphors absorbing at least some of the LED light and emitting adifferent wavelength of light such that the LED emits a combination oflight from the LED and the phosphor. LED chips can be coated with aphosphor using many different methods, with one suitable method beingdescribed in U.S. Pat. Nos. 9,024,349 and 9,159,888, both entitled“Wafer Level Phosphor Coating Method and Devices Fabricated UtilizingMethod”, and both of which are incorporated herein by reference.Alternatively, the LEDs can be coated using other methods such aselectrophoretic deposition (EPD), with a suitable EPD method describedin U.S. Pat. No. 8,563,339 entitled “System for and Method For ClosedLoop Electrophoretic Deposition of Phosphor Materials on SemiconductorDevices”, which is also incorporated herein by reference.

Furthermore, LEDs may have vertical or lateral geometry as is known inthe art. Those comprising a vertical geometry may have a first contacton a substrate and a second contact on a p-type layer. An electricalsignal applied to the first contact spreads into the n-type layer and asignal applied to the second contact spreads into a p-type layer. In thecase of Group-III nitride devices, it is well known that a thinsemitransparent typically covers some or the entire p-type layer. It isunderstood that the second contact can include such a layer, which istypically a metal such as platinum (Pt) or a transparent conductiveoxide such as indium tin oxide (ITO).

LEDs may also comprise a lateral geometry, wherein both contacts are onthe top of the LEDs. A portion of the p-type layer and active region isremoved, such as by etching, to expose a contact mesa on the n-typelayer. A second lateral n-type contact is provided on the mesa of then-type layer. The contacts can comprise known materials deposited usingknown deposition techniques.

FIG. 7 shows one possible embodiment of a LED chip 100 according to thepresent invention. LED chip 100 generally comprises a GaN active region102, a Ni/Ag-based mirror contact 104, a metal barrier 106, an insulator108, and a reflective metal 110. The structure depicted in FIG. 7 isintentionally simplified for illustrative purposes, and it is understoodthat a chip according to the present invention could include additionalcomponents as discussed above or below in more detail and/or as is wellknown in the art, and could likewise include other suitable materials asdiscussed above or below in more detail. Thus, it is understood thatadditional layers and elements can also be incorporated, including butnot limited to buffer, nucleation, contact and current spreading layersas well as light extraction layers and elements. It is also understoodthat the oppositely doped layers can comprise multiple layers andsub-layers, and well as supper lattice structures and inter layers. Theactive region can comprise single quantum well (SQW), multiple quantumwell (MQW), double heterostructure or super lattice structures. Theorder of the layers can be different and in the embodiment shown, thefirst or bottom epitaxial layer can be an n-type doped layer and thesecond or top epitaxial layer can be a p-type doped layer, although inother embodiments the first layer can be p-type doped and the secondlayer n-type doped. Embodiments where the p-type layer is the bottomlayer typically correspond with LEDs that are flip-chip mounted on asubmount. In flip-chip embodiments it is understood that the top layercan be the growth substrate, and in different embodiments all or aportion of the growth substrate can be removed. In those embodimentswhere the growth substrate is removed, the n-type doped layer is exposedas the top surface. In still other embodiments portions of the growthsubstrate can be left, and in some embodiments can be shaped or texturedto enhance light extraction.

Each of the LEDs in the chips discussed herein can have first and secondcontacts, and in the embodiment shown in FIG. 7 , the LED has lateralgeometry. As such, the LED can be contacted from one side or surface ofthe LED, instead of top and bottom surfaces as is the case for verticalgeometry. The first and second contacts can comprise many differentmaterials such as gold (Au), copper (Cu) nickel (Ni), indium (In),aluminum (Al), silver (Ag), or combinations thereof. Still otherembodiments can comprise conducting oxides and transparent conductingoxides such as indium tin oxide, nickel oxide, zinc oxide, cadmium tinoxide, titanium tungsten nickel, indium oxide, tin oxide, magnesiumoxide, ZnGa₂O₄, ZnO₂/Sb, Ga₂O₃/Sn, AgInO₂/Sn, In₂O₃/Zn, CuAlO₂, LaCuOS,CuGaO₂ and SrCu₂O₂. The choice of material used can depend on thelocation of the contacts as well as the desired electricalcharacteristics such as transparency, junction resistivity and sheetresistance.

Some embodiments of LED chips according to the present invention canhave other features, and Group-Ill nitride based LEDs, for example, canhave other features to assist in spreading current from the contacts.This is particularly applicable to spreading current into p-typeGroup-Ill nitrides and the current spreading structure can comprise thinsemitransparent current spreading layer covering some or the entirep-type layer. These layers can comprise different materials includingbut not limited to a metal such as platinum (Pt) or a transparentconductive oxide such as indium tin oxide (ITO).

Submounts can be formed of many different materials such as silicon,ceramic, alumina, aluminum nitride, silicon carbide, sapphire, or apolymeric material such as polyamide and polyester etc. In otherembodiments the submount can include a highly reflective material, suchas reflective ceramics, dielectrics or metal reflectors like silver, toenhance light extraction from the component. In other embodiments thesubmount can comprise a printed circuit board (PCB), or any othersuitable material, such as T-Clad thermal clad insulated substratematerial, available from The Bergquist Company of Chanhassen, Minn. ForPCB embodiments different PCB types can be used such as standard FR-4metal core PCB, or any other type of printed circuit board.

In LED chip 100, the barrier layer 106 does not wrap around the edges ofthe mirror 104 as it does in the prior art. Instead, the barrier layer106 is patterned smaller than the mirror 104 such that it is not exposedto the light emitted toward the mirror or trapped inside the GaN region102. In some embodiment, most of the barrier 106 may be removed in atleast one embodiment so long as the insulator 108 fulfills the duties ofthe barrier 106. The areas of the mirror 104 no longer bordered by thebarrier 106 are instead surrounded by insulator 108, with the insulatorbeing crucial for preventing Ag migration from the mirror 104. As such,the insulator 108 preferably has high density, high bond strength, lowmoisture permeability, and high resistance to metal ion diffusion.Additionally, the interface between the insulator 108 and the GaN region102 is critical, as a weak interface can lead to Ag migration despitehaving an insulator 108 of high quality. Moreover, the insulator 108 maybe optically transparent, and helps space the reflective metal layer 110from the mirror 104.

Below the insulator 108, a reflective metal layer 110 may also bedisposed such that it forms a composite barrier with the insulator andpreferably has significantly higher reflectivity than the metal barrier106. Any light incident on the composite barrier at high angles mayexperience total internal reflection at the GaN/insulator interface dueto the refractive index difference, while low angle light may getreflected off the bottom reflective layer 110. The reflective layer 110preferably consists of a high reflectivity metal such as Al or Ag,although it is understood that other suitable materials may also beused. The reflectivity of the composite barrier may be greater than 80%,or alternatively may be greater than 90%.

The insulator 108 may have low optical absorption and a low refractiveindex in order for the composite barrier to be highly reflective. Sincethe optical and reliability requirements of the insulator 108 may be atodds with one another, the insulator may comprise two or more distinctlayers (not shown). For example, the insulator 108 may comprise a thinlayer having properties optimized to prevent Ag migration in placeswhere it is in contact with the mirror 104 and the GaN region 102, andthe insulator 108 may comprise a second, thicker layer having a lowindex of refraction in between the reflective metal 110 and the thinlayer. As such, total internal reflection can occur at the interfacebetween the thin and thick insulator layers, provided the thicker layeris at least a few optical wavelengths thick. A suitable thickness forthe thick insulator layer may be between 0.5-1 μm. In another example,the insulator 108 may comprise three distinct layers, such as the firsttwo as discussed above and a third layer in between the thick layer andthe reflective metal layer 110, with the third layer being optimized forgood adhesion to the reflective metal layer 110. In yet a furtherexample, a composite barrier may comprise more than three insulatorlayers, in which reflectivity of the composite barrier is furtherincreased by alternating high and low refractive index insulatormaterials.

The insulator 108 may be comprised of many different suitable materials,including an oxide, nitride, or oxynitride of elements Si or Al. Ininsulators comprising two layers as discussed above, the first layer maybe comprised of an oxide or oxynitride of Ti or Ta, while the second,thicker layer may be comprised of a low refractive index material suchas SiO₂. In insulators comprising three layers, the materials may be thesame as a two-layer insulator, with the third layer adjacent thereflective metal layer 110 comprised of SiN. While these materials fitthe requirements for single or multiple layer insulators as discussedabove, it is understood that other suitable materials may also be usedand contemplated in the context of the present invention.

FIG. 8 depicts another embodiment of a LED chip 120 according to thepresent invention. The chip 120 may comprise all the components asdiscussed with chip 100. Also, as described with chip 100, LED chip 120comprises a GaN region 122, an Ag-based mirror 124, a metal barrier 126,an insulator 128, and a reflective metal layer 130. However, FIG. 8further depicts a p-contact being connected to a location outside thejunction through a via connection 132. As indicated above, the mirror124 may also serve as the p-contact for the LED. For purposes ofconnecting the p-contact to a location outside the junction, the metalbarrier 126 may go outside the periphery of the mirror 124 and the GaNregion 122 junction. This section can then be coupled to the viaconnection 132, so that an electrical signal applied to the mirror 124conducts through the via 132 to the extending portion (illustrated bythe crosshatched portion 127 of the barrier 126) and to the GaN region.If the section of the metal barrier 126 extending outside the peripheryof the mirror 124 is sufficiently small and narrow compared to theoverall length of the mirror's periphery, then the poor reflectivity ofthe barrier 126 will have a negligible impact on light extraction. Inone embodiment, the width of the barrier 126 portion 127 outside themirror 124 periphery is ˜20 μm or less.

FIG. 9 depicts another embodiment of a LED chip 140 according to thepresent invention, with chip 140 being a multi-junction chip. Providingsuch a multi-junction chip is one way to get an array of LEDs havinghigh output on higher voltages. The chip 140 may comprise all thecomponents as discussed with chip 100. Also, as described with chip 100,LED chip 140 comprises GaN regions 142, Ag-based mirrors 144, metalbarriers 146, an insulator 148, and a reflective metal layer 150.However, FIG. 9 further depicts a p-contact being connected to then-contact 154 of an adjacent junction.

As indicated above, the mirror 144 may also serve as the p-contact forthe LED. For purposes of connecting the p-contact to the n-contact 154of an adjacent junction, the metal barrier 146 may go outside theperiphery of the mirror 144 and the GaN region 142 junction. If thesection 147 of the metal barrier 146 extending outside the periphery ofthe mirror 144 is sufficiently small and narrow compared to the overalllength of the mirror's periphery, then the poor reflectivity of thebarrier 146 will have a negligible impact on light extraction.Furthermore, the portion 147 of the metal barrier 146 may also be usedto form a wire bond for connecting the p-contact to a package terminal.It is also noted that the metal barrier 146 does not have to cover amajority of the underside of the mirror 144 as depicted in the figures.In some embodiments, the mirror 144 may be substantially eliminated, andcan be in contact with the mirror 144 in only a small section sufficientto form a good electrical contact.

LED chip 140 further comprises passivation layers 152, with thecharacteristics of passivation layers well known in the art. Thepassivation layers 152 may be comprised of SiN, which is a suitablematerial for providing moisture resistance to the chip. However, it isunderstood that other appropriate materials may be used, such as SiO₂.SiO₂ is not as moisture resistant as SiN.

FIG. 10 depicts a monolithic LED chip comprising a plurality of LEDs anda plurality of contact vias 162 as is discussed in more detail belowwith respect to FIG. 12 . When compared to FIG. 6 , it can be readilyobserved that the dark circles in FIG. 6 caused by the exposed portionof barrier layers 64 have been virtually eliminated in FIG. 10 . This isbecause the barrier layers in FIG. 10 (not viewable from thisperspective), have been made smaller than the mirror layers, and arethus not exposed and/or are minimally exposed at the periphery of saidmirrors. Due to the reduction of the exposed barrier layers, any dimmingeffects of the barrier layers are substantially reduced and/oreliminated.

FIG. 11 depicts another embodiment of a LED chip 200 according to thepresent invention. The chip 200 may comprise all the components asdiscussed with chip 100. FIG. 11 may further include a roughened n-GaNlayer 202, a p-GaN layer 204, a mirror layer 206 (which may also serveas the p-contact for the LED), a barrier layer 208, a dielectric barrierlayer 210, a bond metal layer 212, a carrier layer 214, a AuSn layer216, passivation layers 218, 220 (with layer 220 at least partiallyroughened), and n-contacts 222, 224 on the roughened GaN layer. Asdiscussed above, the roughened layers help with light extraction.

As illustrated, the barrier layer 208 in FIG. 11 is sized smaller thanthe mirror 206. As discussed above, such sizing of the barrier layerhelps eliminate many of the light-absorbing effects inherent in layer208, which in turn improves the overall emission and efficiency of theLED chip 200. In this embodiment (as well as in others), thecharacteristics of barrier layer 208 may allow it to act as a currentspreading layer as well as a barrier for Ag migration and/or aprotective layer for mirror 206, such that bond metal layer 212 isisolated from mirror 206 and thus does not dissolve into mirror 206.Bond metal layer 212 may be at least partially comprised of tin, whichmay otherwise dissolve into the mirror 206 but for the barrier 208. Bondmetal layer 212 may further be reflective, although it may not be ashighly reflective as mirror 206.

Passivation layers 218 are disposed on the sidewalls of the activeregion, providing sidewall passivation as is well known in the art.Passivation layers 218 may be comprised of SiN, which exhibits favorablemoisture resistive characteristics. However, it is understood that othersuitable materials are also contemplated. Passivation layer 220 may alsobe disposed over the device as shown to provide physical protection tothe underlying components. Passivation layer 220 may be comprised ofSiO₂, but it is understood that other suitable passivation materials arealso contemplated.

The dielectric barrier layer 210 is provided, at least in part, toprotect/isolate the mirror 206 and portions of barrier 208 from the bondmetal layer 212. The dielectric layer may be transparent, and/or maycomprise different dielectric materials such as SiN, SiO₂, Si, Ge, MgOx,MgNx, ZnO, SiNx, SiOx, alloys or combinations thereof. The dielectriclayer 210 may also extend further under barrier 208 as depicted by thecrosshatched sections under barrier 208.

FIG. 12 depicts another embodiment of a LED chip 230 according to thepresent invention. The chip 230 may comprise some or all of thecomponents as discussed with the other chip embodiments. However, thebiggest difference between chip 230 and the other chip embodiments isthat n-contact vias are provided as shown in FIG. 12 , with the vias notshown in FIG. 13 for ease of illustration. The vias allow for theremoval of the n-contact metal on the topside of the device and then-contact is essentially embedded within the device and electricallyaccessibly from the bottom of the chip. With less topside metal to blocklight emission, improved brightness can be realized. Furthermore, thebarrier metal outside the periphery of the mirror is eliminated and/orsubstantially reduced, which further contributes to the emissionefficiency of the device.

The vias according to the present invention can be formed usingconventional methods, such as etching to form the openings for the viasand photolithographic processes for forming the via. The vias take onlya fraction of the area on the LED chip that would be needed for a wirebond pad. By using one or more vias in place of a wire bond pad, less ofthe active area is removed and fewer emission blocking metal forcontacts is located on the topside of the device. This leaves more LEDactive area for light emission, thereby increasing the overallefficiency of the LED chip.

It is also understood that different embodiments can have more than onevia and the vias can be in many different locations. In thoseembodiments having multiple vias, the vias can have different shapes andsizes and can extend to different depths in the LED. It is alsounderstood that different embodiments can also comprise vias used inplace of the first wire bond pad.

FIG. 12 may further include a roughened n-GaN layer 232, p-GaN layers234, mirror layers 236 (which may also serve as the p-contact for theLED), barrier layers 238, passivation layers 240, 241, an n-contact 242,barrier layer 244, a bond metal layer 246, a carrier layer 248, AuSnlayer 250, and passivation layer 252. As discussed above, the roughenedlayers assist with improved light extraction of the device.

As with other embodiments discussed herein, the barrier layers 238 aresized such that they are smaller than the mirror layers 236 and/or areprevented from extending beyond 40% or more of the periphery of themirrors 236. The barrier layers 238 may be further provided to form acontact at the topside of the device for the p-contact integral to atleast a portion of mirrors 236. As best shown in Furthermore, thebarrier layers 238 may help spread current laterally through the devicesince the mirrors 236 may be too thin to effectively spread current.

The barrier layer 244 may be provided as a protective layer forn-contact 242, such that bond metal layer 246 is isolated from n-contact242 and thus does not dissolve into or otherwise adversely react withn-contact 242. Barrier layer 244 may be comprised of TiW/Pt, although itis understood that other suitable materials are contemplated. In someembodiments, barrier layer 244 may not be necessary depending on thematerial make-up of the n-contact 242 and bond metal layer 246. Then-contact may be comprised of a variety of suitable materials, withpreferred materials being reflective to further enhance the lightemission of the device. As such, n-contact 242 may be comprised of Al,Ag, or other reflective materials. Bond metal layer 246 may further bereflective.

Passivation layers 241 are disposed on the sidewalls of the activeregion, providing sidewall passivation as is well known in the art.Passivation layers 240, 241 may be comprised of SiN, which exhibitsfavorable moisture resistive characteristics. However, it is understoodthat other suitable materials are also contemplated. Passivation layer252 may also be disposed over the device as shown to provide physicalprotection to the underlying components. Passivation layer 252 may becomprised of SiO₂, but it is understood that other suitable passivationmaterials are also contemplated.

FIG. 13 is a top view of the LED chip 230 shown in FIG. 12 , with FIG.13 showing the n-type layer 234 and the outer edge of the mirror 236below the n-type layer and in phantom. FIG. 13 also shows the outeredges of the barrier layer 238 with the areas not exposed shown inphantom as further described below. The remaining layers, vias and inneredges of the barrier layer and mirror layers are not shown for ease ofillustration. As mentioned above a portion of the barrier layer 238 mayserve as the p-type contact at the topside of the device. In someembodiments a portion of the barrier layer can be exposed for contactingand in the embodiment shown the LED chip layers can be removed above aportion of the barrier layer. In one embodiment the layers above thebarrier layer 238 can be etched to the barrier layer 238, therebyforming an exposed barrier layer region 260. The exposed region 260 canbe in many different locations and can have many different shapes, withthe embodiment shown being at a corner of the LED chip 230.

Exposing the barrier layer in this manner provides advantages such asease of contacting, but can also present the danger of moisture orcontaminants entering the LED layers along the surfaces or edges in theexposed region 260. This moisture or contaminants can negatively impactthe lifetime and reliability of an LED chip. To help reduce this danger,steps or transitions can be included as part of the barrier layer thatcan inhibit or eliminate the amount of moisture or contaminants that canenter the LED chip. The steps or transition can take many differentshapes and sizes. Different LED chips can have different numbers ofsteps or transitions and they can be included in different locations onthe barrier layer. In still other embodiments, steps or transitions canbe included in other layers.

FIG. 14 shows another embodiment of an LED chip 270 that is similar tothe LED chip 230 shown in FIGS. 12 and 13 . The LED chip 270 has ann-type layer 234, mirror layer 236 and barrier layer 272, with the otherlayers and features not shown for ease of illustration. N-type layer 234and mirror layer 236 are similar to those in LED chip 230 as shown inFIG. 13 . Barrier layer 272 is also similar to barrier layer 236 in FIG.13 and can be contacted through the exposed region 274. The barrierlayer 272 has two steps 276 along the edge of the barrier layer 272 thathelp reduce or eliminate moisture or contaminants that can enter the LEDchip 270 along the edge of the barrier layer 272.

For the embodiments shown in both FIGS. 13 and 14 the exposed area ofthe barrier layer results in a portion of the barrier layer beinguncovered such that it may absorb some LED chip light. The amount ofexposed barrier can be minimized to minimize the impact of the lightabsorption, with the periphery of the mirror being free of the barrierlayer in the percentages described above. In some embodiments, theexposed portion of the barrier layer can be less than 20% of the overallbarrier layer surface. In still other embodiments it can be less than10%, while in other embodiments it can be less than 5%.

The barrier layer can have many different shapes and can be arranged indifferent locations relative to the other layers of the LED chipsaccording to the present invention. FIG. 15 shows another embodiment ofan LED chip 280 according to the present invention that is similar tothe LED chip 270, and shows an n-type layer 234 and mirror layer 236. Inthis embodiment, however, the barrier layer 282 extends beyond thatmirror layer 236 along two edges of the mirror layer 236, and thebarrier layer can extend beyond the mirror layers in different locationsof LED chips. To still have the desirable emission efficiency of the LEDchips, the exposed portions of the barrier layers can be relatively thinto reduce the light absorbing surfaces. In some embodiments more than75% of the exposed edges can be less than 3 microns wide. In otherembodiments 90% can have this width, while in other embodiments 100% ofthe exposed edges can have this width. The exposed width for thesepercentages can also be different in other embodiments, such as lessthan 4 microns or less than 2 microns.

The present invention can be used in many different lightingapplications, and in particular those using a small sized high outputlight source. Some of these include, but are not limited to, generalillumination, outdoor lighting, flashlights, white LEDs, streetlights,architectural lights, home and office lighting, display lighting andbacklighting.

Different embodiments of LED chips can be arranged in many differentways and can be used in many different applications according to thepresent invention. Some of these LED chips can comprise one or moreactive regions that can be interconnected in different ways, with someembodiments comprising a plurality of active regions on the samesubmount and interconnected to form high luminous flux emittersoperating from relatively high voltages. In some embodiments, the activeregions can be coupled together in a linear fashion to provide a lightsource similar to a filament source. By providing the active regions ona single submount, the space between adjacent LEDs can be minimized.When the active regions emit during operation, the dark spaces betweenadjacent ones of the active regions can be minimized to give the sourcethe appearance of continual light source.

In some embodiments, the active regions can be formed as a wafer andthen mounted (e.g. flip-chip mounted) on the submount. The submount cancomprise internal electrical interconnects and insulation layers toallow for serial interconnection of LEDs without the need for externalinterconnects such as wire bonds. In other embodiments, the wafer withthe active regions can comprise internal interconnections and/orinsulation layers for interconnection.

In embodiments where the active regions are mounted on the submount inwafer form, the spaces or streets can be formed in the wafer to form theindividual active regions. The active region and submount combinationcan be further processed by dividing or dicing the desired number ofactive regions. For example, an active region and submount combinationwith four linearly arranged active regions could be separated from thewafer active region and submount combination. Contacts can then beformed on the LED chip for applying an electrical signal to the LED chipduring operation.

In still other embodiments, the desired group of active regions can beseparated from the active region wafer and then mounted on the submount.For example, a linear arrangement of four active regions can beseparated from the active region wafer and then mounted (e.g. flip-chipmounted) to a submount appropriately sized and arranged to accept thefour active regions. In still other embodiments, individual activeregions can be mounted on submount.

The monolithic LED chips are described herein with reference to seriesconnections, but it is understood that the active regions can beinterconnected in different series and parallel combinations. Thedifferent embodiments of the present invention can be arranged in manydifferent ways with many different features. Some embodiments cancomprise barrier layers as described above, with the barrier layer insome embodiments not extending, or minimally extending, beyond the edgeof the mirror as described above in certain areas (e.g. below theemission area of the active region). This can help minimize the amountof light absorbed by the barrier layer, thereby increasing overallemission efficiency.

FIG. 16 is a sectional view of one embodiment of a monolithic LED chip300 according to the present invention. The LED chip 300 can comprisemany different features and layers, most of which are not shown for easeof description. The LED chip 300 comprises a plurality of emittingactive regions 302 mounted on submount 304. As mentioned above, in someembodiments the active regions can be mounted on the submount in waferform or portion of the wafer comprising a group of active regions. Instill other embodiments, individual active regions can be mounted to thesubmount 304. In embodiments where an active region wafer or portion ofan active region wafer is mounted to the submount 304, the individualactive regions can be separated on the submount 304 by known methodssuch as etching, cutting or dicing. The side surfaces of the resultingactive regions can be angled or shaped, and the distance betweenadjacent active regions is relatively small. In some embodiments, thedistance can be 15 microns (μ) or less or less, while in otherembodiments it can be 10 μ or less. In still other embodiments, it canbe 5 μ or less, and in other embodiment is can be 1 μ or less. Someembodiments can also have a space in the range of 1 to 0.05 μ. The spacecan have different percentage of a width of the active regions with someembodiments having a space that is approximately 15% or less of anactive region width, while in other embodiments the space can beapproximately 10% or less. In still other embodiments the space can be5% or less of a width, while other embodiments can have a space that is2.5% or less of a width. Other embodiments can have a space that is 1.5%or less of a width, with some embodiments having a space that isapproximately 1.1% of an active region width. These are only some of theratios and dimensions that can be used in different embodimentsaccording to the present invention.

The submount 304 can also contain integral and internal electricalinterconnects 306 arranged to connect the active regions in series. Insome embodiments this can comprise a number of vias and electricallyconductive paths or layers coupled together in different ways to providethe desired interconnect scheme. The LED chip 300 can also comprisefirst and second contact pads 308, 310 for applying an electrical signalto the LED chip 300. The first contact 308 can be either a p-contact oran n-contact, with the second contact 310 being the other of thep-contact and n-contact. In some embodiments, the LED chip 300 alsocomprise contact interconnects 312 for conducting an electrical signalfrom the first contact pad 308 to the first of the active regions 302,and for conducting an electrical signal from the last of the activeregions 302 to the second contact pad 310.

The arrangement allows for an electrical signal to be applied to the LEDchip 300 across the first and second contacts 308, 310. The LED chip 300can also comprise one or more insulating layers 314 to electricallyinsulate the active regions 302 and interconnects 306, 312 from anyconductive elements below the insulating layer 314. In some embodiments,other insulating layers can be included such that at least a portion ofthe interconnects 306, 312 are surrounded by insulating materials, withthose portions buried in the insulating material. The LED chip 300 canalso comprise a substrate 316 and bonding layer 318 for adhesion betweenthe substrate 316 and the layers above the substrate 316.

The LED chip 300 can operate from an electrical signal that isapproximately equal to the sum of the junction voltages of the activeregions 302. Other factors contribute to the operating voltage, with thevoltage generally scaling with the number of junctions. In someembodiments each of the active regions 302 can have a junction voltageof approximately 3 V, such that the electrical signal applied to theactive regions can be approximately equal to 3 times the number ofactive regions. In some embodiments, the LED chip can have four activeregions so that the LED chip operates from an approximate 12 Velectrical signal.

The LED chips according to the present invention can be fabricated inmany different ways according to the present invention. FIG. 17 showsthe LED chip 300 at an intermediate manufacturing step where in someembodiments the active regions can be formed separately from thesubmount 304, with the submount having buried interconnects 306, 312,insulating layer(s) 314 and contacts 308, 310. The active regions 302can then be mounted to the submount in contact with interconnects 306,312. The active regions 302 can then have spaces formed between adjacentones of the active regions, with the spaces formed either before orafter mounting on the submount 304.

FIGS. 18 and 19 show another embodiment of a monolithic LED chip 320having many of the same features as LED chip 300. For these samefeatures, the same reference numbers are used with the understandingthat the description above applies to the features in this embodiment.In this embodiment, the active regions 302 are formed with interconnects306, 312, insulating layer(s) 314 and contacts 308, 310. Like theembodiment above, at least a portion of the interconnects 306, 312 areburied in or surrounded by insulating material to electrically isolatethem from other features in the LED chip 320. This structure can then bemounted to a separate substrate and bonding layer structure 322 to formthe monolithic LED chips 320 with serially interconnected activeregions.

Different LED chip embodiments according to the present invention canhave many different features and layers of different materials arrangedin different ways. FIG. 20 shows another embodiment of a monolithic LEDchip 350 according to the present invention comprising twointerconnected active regions 352, but it understood that othermonolithic LED chips can comprise many different numbers ofinterconnected active regions. The active regions 352 can have lateralgeometry and can be flip-chip mounted on a submount 354 that can havemany different features and can be made of many different layers andmaterials.

The active regions 352 can be made from many different material systems,with the embodiment shown being from a Group-III nitride materialsystem. The active regions 352 can comprise a GaN active structure 356having a p-type layer 358, n-type layer 360 and an active layer 362.Some embodiments of the active regions can also comprise a growthsubstrate that can be many different materials such as silicon carbideor sapphire, and can be shaped or textured to enhance light extractionsuch as the substrate shaping utilized in commercially available DA lineof LEDs from Cree, Inc. In the embodiment shown, the substrate can beremoved and the n-type layer 360 can be shaped or textured to enhancelight extraction.

The active regions 352 can also comprises a current spreading layer 364that is on the p-type layer 358 such that when the active regions 352are mounted on the submount 354, the LED current spreading layer 364 isbetween the active structure 356 and the submount 354. The currentspreading layer 364 can comprise many different materials and istypically a transparent conductive oxide such as indium tin oxide (ITO)or a metal such as platinum (Pt), although other materials can also beused. The current spreading layer 364 can have many differentthicknesses, with the present invention having a thickness small enoughto minimize absorption of light from the active structure that passesthrough the current spreading layer. Some embodiments of the currentspreading layer 364 comprise ITO having thicknesses less than 1000angstroms (Å), while other embodiments can have a thickness less than700 Å. Still other embodiments can have a thickness less than 500 Å.Still other embodiments can have a thickness in the range of 50 to 300Å, with some of these embodiments having current spreading layer 364with a thickness of approximately 200 Å. The current spreading layer 364as well as the reflective layers described below can be deposited usingknown methods. It is understood that in embodiments where currentspreading is not a concern, the active regions can be provided without acurrent spreading layer.

A low index of refraction (IR) reflective layer 366 can be arranged onthe current spreading layer 364, with current spreading layer 364between the reflective layer 366 and active structure 356. Thereflective layer 366 can comprise many different materials andpreferably comprises a material that presents an IR step between thematerials comprising the active structure 356. Stated differently, thereflective layer 366 should have an IR that is smaller than the activestructure to promote TIR of active structure light emitting toward thereflective layer 366. Light that experiences TIR can be reflectedwithout experiencing absorption or loss, and TIR allows for theefficient reflection of active structure light so that it can contributeto useful or desired active region emission. This type of reflectivelayer can be an improvement over devices that rely on metal layers toreflect light where the light can experience loss with each reflection.This can reduce the overall LED chip emission efficiency.

Many different materials can be used for the reflective layer 366, withsome having an IR less than 2.3, while other embodiments can have an IRless than 2.15. In still other embodiments the IR can be less than 2.0.In some embodiments the reflective layer 366 can comprise a dielectric,with some embodiments comprising SiO₂. It is understood that otherdielectric materials can be used such as SiN, Si, Ge, MgOx, MgNx, ZnO,SiNx, SiOx, AIN, and alloys or combinations thereof.

Some Group III nitride materials such as GaN can have an IR ofapproximately 2.4, and SiO₂ has an IR of approximately 1.46. Embodimentswith an active LED structure 356 comprising GaN and that also comprisesa SiO₂ reflective layer, can have a sufficient IR step between the twoto allow for efficient TIR of light at the junction between the two. Thereflective layer 366 can have different thicknesses depending on thetype of material, with some embodiments having a thickness of at least0.2 microns (μm). In some of these embodiments it can have a thicknessin the range of 0.2 to 0.7 μm, while in some of these embodiments it canbe approximately 0.5 μm thick.

As light experiences TIR at the junction with the reflective layer 366an evanescent wave with exponentially decaying intensity can extend intothe reflective layer 366. This wave is most intense within approximatelyone third of the light wavelength from the junction (about 0.3 um for450 nm light in SiO₂). If the reflective layer 366 is too thin, suchthat significant intensity remains in the evanescent wave at theinterface between the first reflective layer 366 and the secondreflective layer 368, a portion of the light can reach the secondreflective layer 368. This in turn can reduce the TIR reflection at thefirst interface. For this reason, in some embodiments the reflectivelayer 366 should have a thickness of at least 0.3 um.

A metal reflective layer (i.e. second reflective layer) 368 and adhesionlayer 370 are included on the reflective layer 366, with the adhesionlayer 370 sandwiched between and providing adhesion between the metallayer 368 and reflective layer 366. The metal layer 368 is arranged toreflect light that does not experience TIR at the junction with thereflective layer 366 and passes through the reflective layer 366. Themetal layer 368 can comprise many different materials such as Ag, Au,Al, or combinations thereof, with the present invention being Ag.

Many different materials can be used for the adhesion layer 370, such asITO, TiO, TiON, TiO₂, TaO, TaON, Ta₂O₅, AlO or combinations thereof,with a preferred material being TiON. The adhesion layer 370 can havemany different thicknesses from just a few Å to thousands of Å. In someembodiments it can be less than 100 Å, while in other embodiments it canbe less than 50 Å. In some of these embodiments it can be approximately20Å thick. The thickness of the adhesion layer 370 and the material usedshould minimize the absorption of light passing to minimize losses oflight reflecting off the metal layer 368.

The active regions 352 can further comprise reflective layer holes 372that can pass through the adhesion layer 370 and the reflective layer366, to the current spreading layer 364. The holes 372 can then befilled when the metal layer 368 is deposited with the metal layermaterial forming vias 374 to the current spreading layer 364. The vias374 can provide a conductive path through the reflective layer 368,between the p-contact and the current spreading layer 364.

The holes 372 can be formed using many known processes such asconventional etching processes or mechanical processes such as microdrilling. The holes 372 can have many different shapes and sizes, withthe holes 372 in the embodiment shown having angled or curved sidesurfaces and a circular cross-section with a diameter of less than 20μm. In some embodiments, the holes 372 can have a diameter ofapproximately 8 μm, with others having a diameter down to 1 μm. Adjacentholes 372 can be less than 100 μm apart, with the embodiment shownhaving a spacing of 30 μm spacing from edge to edge. In still otherembodiments, the holes can have a spacing of as low as 10 μm or less. Itis understood that the holes 372 (and resulting vias) can havecross-section with different shapes such as square, rectangular, oval,hexagon, pentagon, etc. In other embodiments the holes are not uniformsize and shapes and there can be different or non-uniform spaces betweenadjacent holes.

In other embodiments different structures can be used to provide aconductive path between the p-contact and the current spreading layer.Instead of holes an interconnected grid can be formed through thereflective layer 368, with a conductive material then being deposited inthe grid to form the conductive path through the composite layer. Thegrid can take many different forms, with portions of the gridinterconnecting at different angles in different embodiments. Anelectrical signal applied to the grid can spread throughout and alongthe interconnected portions. It is further understood that in differentembodiments a grid can be used in combination with holes, while otherembodiments can provide other conductive paths. In some embodiments oneor more conductive paths can run outside the LED chip's active layersuch as along a side surface of the LED chip.

The active regions 352 can also comprise a barrier layer 376 on themetal layer 368 to prevent migration of the metal layer material toother layers. Preventing this migration helps the LED chips 352 maintainefficient operation through their lifetime.

An active structure hole 378 can be included passing through the barrierlayer 376, metal layer 368, adhesion layer 370, reflective layer 366,and p-type layer 358, to expose the n-type layer 360. A passivationlayer 380 is included on the barrier layer 376 and the side surfaces ofthe active structure hole 378. The passivation layer 380 protects andprovides electrical insulation between the contacts and the layers belowas described in more detail below. The passivation layer 380 cancomprise many different materials, such as a dielectric material. In theembodiment shown, the barrier layer 376 does not extend beyond the edgeof the metal layer 368 around the active structure hole 378. Thisreduces the amount of light absorbing barrier layer material that wouldabsorb LED light, thereby increasing the overall emission efficiency ofthe LED chip 350.

For one of the active regions 352, the barrier layer 376 can extendbeyond the edge of the active region 352 and can be exposed at a mesa onthe passivation layer 380 adjacent the LED. This exposed portion can beused for contacting the serially interconnected active regions 352. Insome embodiments, a p-contact pad 382 can be deposited on thepassivation barrier layer 376, with the p-contact 382 providing anelectrical signal that can pass to the p-type layer 358. An electricalsignal applied to the p-contact passes through the barrier layer 376,the metal layer 368, the vias 374, and to the current spreading layer364 through which it is spread to the p-type layer 358.

An n-contact 384 can be formed on the n-type layer 360 and a conductiven-type layer vias 388 can be formed through the passivation layer 380and between the n-type contact 384 and an interconnection metal layer386. As more fully described below, the interconnection metal layer 386is arranged to conduct an electrical signal between adjacent ones of theLED chips 352 to interconnect them in series. The interconnection metallayer 386 can have breaks along its length to facilitate this serialinterconnection and can be made of many electrically conductivematerials, such as those described herein. As described above, the metallayer 386 can be formed as part of the submount 354 using known methods,and can be formed with the active regions. An electrical signal at then-type layer 360 conducts into the n-contact 384, into its correspondingvia 388, and to the interconnection metal layer 386. The interconnectionlayer can have many different shapes and thicknesses. In someembodiments it can comprise a substantially continuous layer withbreaks, while in other embodiment it can comprise conductive traces.

The p-contact 382, the n-contact 384, interconnection metal layer 386,and n-type vias 388 can comprise many different materials such as Au,copper (Cu) nickel (Ni), indium (In), aluminum (Al), silver (Ag), tin(Sn), platinum (Pt) or combinations thereof. In still other embodimentsthey can comprise conducting oxides and transparent conducting oxidessuch as ITO, nickel oxide, zinc oxide, cadmium tin oxide, indium oxide,tin oxide, magnesium oxide, ZnGa₂O₄, ZnO₂/Sb, Ga₂O₃/Sn, AgInO₂/Sn,In₂O₃/Zn, CuAlO₂, LaCuOS, CuGaO₂ and SrCu₂O₂. The choice of materialused can depend on the location of these features as well as the desiredelectrical characteristics such as transparency, junction resistivityand sheet resistance.

As mentioned above, the growth substrate for active regions 352 has beenremoved, and the top surface of the n-type layer is textured for lightextraction. The active regions 352 are flip-chip mounted to a substrate390 that can provide mechanical stability. A bond metal layer 392 andblanket mirror 394 between the substrate 390 and the active structure356. The substrate 390 can be made of many different materials, with asuitable material being silicon. The blanket mirror 384 can be made ofmany different materials, with a suitable material being Al. The blanketmirror 384 helps to reflect LED light that escapes reflection by thereflective layer 366 and the metal layer 368, such as light that passesthrough the active structure hole 378.

The reflective layer 366 and the metal layer 368 are arranged betweenthe active region's active structure 356 and the substrate 390 so thatlight emitted by the active structure 356 toward the substrate 390 canbe reflected back to contribute to useful LED light emission. Thisreduces the amount of light that can be absorbed by structures such asthe substrate 390, with the embodiments according to present inventionpromoting reflection by TIR instead of reflection off metal layers, tofurther reduce light loss due to absorption.

The submount 354 also comprises an isolation layer 396 arranged on theblanket mirror 394 such that it provides electrical isolation betweenthe blanket mirror 394 and all elements above the blanket mirror 394,such as the interconnection metal 386. This isolation allows forelectrical signals to be conducted between adjacent ones of the activeregions without being shorted to the blanket mirror 394 or otherfeatures below the blanket mirror 394. The isolation layer 396 can bemade of many different materials, with the preferred material being madeof an electrically insulating material such as a dielectric. Thecombination of the isolation layer 396 and passivation layer 380 resultsin the interconnection metal 386 being buried and/or surrounded byelectrically insulating materials. This internal isolation of theelectrical paths within the LED chip 350 provides for reliable andefficient interconnection and operation of the active regions 352.

As mentioned above, an electrical signal is applied to the p-type layer358 in the first of the active regions connected in series, at thep-type contact pad 382. For each of the subsequent active regions 352connected in series, a p-type conductive vias 398 is included betweenthe interconnection metal layer 386 and the barrier layer 376 of theactive region. The electrical signal at the vias 398 passes through thebarrier layer 376 and to the current spreading layer 364 and to thep-type layer 358.

At the last of the serial connected actives regions, and n-contact pad400 is formed on a mesa on the passivation layer 380 adjacent the activeregion 352. An n-pad via 402 is formed between the n-contact pad 400 andthe interconnection metal layer to conduct a signal from the n-typelayer 360 in the last of the LED chips 352 to the n-contact pad 400. Theemitter 350 can also comprise a passivation or protection layer 406 onthe side surfaces of the active structure 356 and covering the topsurface of the submount 354 around the p-contact pad 382 and then-contact pad 400.

FIG. 21 shows the LED chip 350 during operation with an electricalsignal following a path through the emitter 350 as shown by arrows 404.An electrical signal is applied to the p-contact pad 382 and isconducted through the barrier layer 376, metal layer 368, and currentspreading layer 364, to the p-type layer 358. The signal then passesthrough to the n-type layer 360 where it passes through to the n-contact384 and the n-type vias 388. The signal then conducts along theinterconnection metal layer where it passes into the first of the p-typevias 398. The signal is then conducted to the p-type layer 358 in thesecond active region 352, where it passes into the n-type layer 360,n-contact 384 and n-type vias 388. Although only two active regions 352are shown, it is understood that emitters according to the presentinvention can have many more, and in those embodiments, the signal thenpasses on to the next of the active regions 352 connected in series andthis continues until the last of the active regions 352. At the last ofthe active regions 352, the electrical signal at the n-type vias 388passes into the interconnection metal layer 386 and to the n-pad vias402, where it is conducted to the n-contact pad 400. This type ofinterconnection and current flow allows for a high voltage LED chiplight source formed monolithically on a submount.

The LED chip 350 shown in FIGS. 20 and 21 comprises a lateral geometryin that electrical signals can be applied to the LED chip 350 atp-contact 382 and n-contact pad 400 accessible from the top surface ofthe LED chip. In other embodiments the LED chip 350 can comprisedifferent contact geometries and arrangements. FIGS. 22 and 23 showanother embodiment of an

LED chip 450 according to the present invention having many of the samefeatures as the LED chip 350, but having internal conductive features toprovide a vertical geometry chip. The LED chip does not have ann-contact pad on its top surface, but instead a substrate via 452 thatpasses from the interconnection metal layer 386, down and through theinsulation layer 396, to the layers below. In embodiments where thesubstrate 390, bond metal layer 392, and blanket mirror 394 compriseelectrically conductive materials, the substrate vias 452 can extend tothe blanket mirror 452. An electrical signal applied to the substrate390 would conduct to the substrate via 452. In embodiments where one ofthese layers does not have the desired electrical conductivity, the canpass further through the different layers. For example, if the substrate390 is not electrically conductive, the substrate vias 452 can passthrough the substrate 390 so that it is accessible at the bottom of theLED chip 450. One or more contact layers or pads (not shown) can also beincluded on the bottom of the LED for making electrical contact.

Referring now to FIG. 23 , an electrical signal passes through the LEDchip 450 as shown by arrows 454, and has much the same path as thatshown for LED chip 350 in FIG. 21 . An electrical signal is applied tothe p-contact pad 382 and is conducted through the barrier layer 376,metal layer 368, and current spreading layer 364, to the p-type layer358. The signal then passes through to the n-type layer 360 where itpasses through to the n-contact 384 and the n-type vias 388. The signalthen conducts along the interconnection metal layer 386 where it passesinto the first of the p-type vias 398. The signal is then conducted tothe p-type layer 358 in the second active region 352, where it passesinto the n-type layer 360, n-contact 384 and n-type vias 388. The signalthen passes on to the next of the active regions 352 connected in seriesand this continues until the last of the active regions 352. At the lastof the active regions 352, the electrical signal at the n-type vias 388passes into the interconnection metal layer 386 and to the substratevias where it passes to the substrate 390. This type of an electricalsignal to be applied to the LED chip at the top surface (p-contact pad382) and the bottom surface (substrate 390) in a vertical geometry typearrangement.

It is understood that the above are only examples of differentinterconnection and contacting arrangements according to the presentinvention. Other embodiments can have different internal interconnectionarrangements and other embodiment can be arranged so that an electricalsignal is applied to the LED chip at the bottom surface. It is alsounderstood that all of the embodiments described above can also beincluded in vertical geometry type LED packages.

The monolithic LED chips can be used in many different applications andcan be arranged in many different ways. FIG. 24 shows one embodiment ofa monolithic LED chip 500 according to the present invention thatcomprises four active regions 502 arranged on a single submount 504. TheLED chip 500 can have many different shapes and sizes, with the emittershown having a rectangular shape. Each of the active regions 502 canalso have a generally rectangular footprint, with a small space 506formed between adjacent ones of the active regions 502. The space 506 isshown as being in a straight line, but it is understood that the spacecan have curves or can be squiggly. The space 506 can be formed usingknown methods such as different etch or cut methods. A p-contact pad 508is arranged at one end of the emitter 500 and the n-contact pad 510 isarranged at the opposite end. A signal applied to the p-contact padconducts through the device to the n-contact as described above.

The different embodiments of the devices described herein can have manyadvantages. The rectangular embodiment can be sized to mimic theemission of a filament in a convention light source. By interconnectingthe active regions in series, a high voltage light source can beprovided that is compatible with many conventional lightingapplications. In the embodiment shown, the emitter 450 has four activeregions each having a 3 volt junction. This results in the LED chip 450comprising a 12 volt light source. Different numbers of LEDs can resultin emitters that operate from different voltages. For example, asimilarly arranged emitter with six active regions comprises a 24 voltlight source.

By providing a monolithic device formed on a single substrate instead ofdiscrete LED chips or packages on a submount, the space between adjacentactive regions can be minimized. This minimizes or eliminates theundesirable dark spaces between adjacent ones of the active regions,giving the emitter the appearance of a continuous filament.

The monolithic emitters can be used in many different lighting fixtures,including but not limited to lamps, bulbs, flashlight, streetlights,automobile headlights, etc. FIG. 25 shows one embodiment of a carheadlight 550 according to the present invention having a housing 552,with an opening having a light transmitting cover/lens 554. Theheadlight has one or more monolithic LED chips 556 mounted in thehousing so that light from LED chips emits out the housing openingthrough the lens/cover. Many different monolithic LED chips can be usedwith many different numbers of active regions, with some embodimentsusing a four active region monolithic LED chip operating from a 12 velectrical signal

For high voltage LED chips that connect multiple p-n junctions togetheron a single chip as described above (e.g. through wafer fabricationprocessing), the integral nature of the interconnection metal layers canpresent certain problems during operation. For example, when the LEDchips are used in high power applications, they can experience certainreliability problems. In some embodiments, the interconnection metallayers 386 in a high voltage chip function as current carrying layerswhile also being a reflective layer. The layer 386 should comprise agood current conductor that is also reflective so that it does notabsorb LED light. Different materials can comprise both theseproperties, such as Al or Ag. One potential problem is that some ofthese interconnection metal layers made of these materials canexperience electromigration under high current operation that can causedegradation in performance and can ultimately lead to failure of thedevice. In some instances this electromigration can cause voids in theinterconnecting layer that can degrade performance of the LED chip.These voids that can then result in current conducting hot spots, whichcan accelerate electromigration. Continued electromigration caneventually lead to open circuits in the interconnect layer and failureof the LED chip.

To address this issue, some embodiments according to the presentinvention can have layer structures or interconnection metal layers madeof certain materials, with both helping to reduce or eliminate thisinterconnection metal layer electromigration. This can result in morereliable devices where failures under high power operation aremitigated. These LED chips can experience longer lifetimes and improvedperformance throughout their lifetime.

The present invention can be applied to many different LED chipsoperating from different power densities. In some embodiments, the LEDchips can operate with power density up to 3 watts per square millimeter(W/mm²). Other embodiments can operate with even higher power density upto 10 W/mm², while still other embodiments can operate with powerdensity in excess of 10 W/mm².

Operating at higher power density can lead to devices operating athigher temperature, and there can also be other causes of hightemperature operation such as environmental conditions. The embodimentsaccording to the present invention can reliably operate at hightemperature, with some embodiments capable of reliable operation atjunction temperatures up to 85° C. Other embodiments according to thepresent invention can reliably operate at junction temperatures up to125° C., while other embodiments can reliably operate at junctiontemperatures up to 200° C. Still other embodiments can reliably operateat junction temperatures high than 200° C.

The present invention can also be used in many different chip sizes.Chip size ranges can be defined in terms of the area of the chip andsome embodiments can have chip area of up to 1 mm². Other embodimentscan have chip area up to 6 mm², while other embodiments can have largerchip areas.

FIG. 26 shows another embodiment of an LED chip 600 according to thepresent invention having an interconnection metal layer arranged toreduce or eliminate high power performance degradation and failure dueto electromigration. In this embodiment, the interconnection metallayer's functions of reflector and electrical conductor can be separatedinto different layers. This allows for an interconnection metal layerthat efficiently conducts electrical signals, but also has highresistance to electromigration. This high resistance to electromigrationresults in little to no electromigration and reduces or eliminates theelectromigration related failures described above. Some conductivematerials with high resistance to electromigration may have lowerreflectivity, which can cause these layers to absorb LED chip light andlower overall LED chip emission efficiency. To address this, these LEDchip embodiments can also have reflective/reflector layers or featuresthat are separate from the conductive interconnect layer and arearranged to reflect light that might otherwise be absorbed by the lessreflective interconnection metal layer. This reflected light cancontribute to over LED chip emission to provide for efficient overallLED chip emission efficiency.

LED chip 600 has many of the same or similar features and the LED chipsshown in FIGS. 20-23 and described above, and for these features thesame reference numbers are used. It is understood that these same orsimilar features can be arranged in the same way and can comprise thesame materials with the same or similar dimensions as those describedabove. The LED chip 600 comprises active regions 352 on a submount 354,with the active regions comprising active structures 356 with p-typelayer 358, n-type layer 360 and active layer 362. A current spreadinglayer (or p-contact layer) 364 is included on the p-type layer, and afirst low index of refraction reflective layer 366 is included on thecurrent spreading layer 364. A second reflective layer 368 in includedon the first reflective layer 366, with an adhesion layer 370 betweenthe two reflective layers. Reflective layer holes 372 are includedthrough the first reflective layer with vias 374 formed through thefirst from reflective layer 366 from the second reflective layermaterial. An electrical signal carried by the second reflective layer368 passes through the first reflective layer 366 along vias 374 and tothe current spreading layer 364.

A barrier layer 376 can be included on the second reflective layer 368to help prevent electromigration of the second reflective layer materialto other layers. This also helps maintain reliable and efficientoperation of the LED chip 600. An active structure hole 378 can beincluded passing through the barrier layer 376, metal layer 368,adhesion layer 370, reflective layer 366, and p-type layer 358, toexpose the n-type layer 360. A passivation layer 380 is included on thebarrier layer 376 and the side surfaces of the active structure hole378. In this embodiment, the barrier layer 376 can extend beyond theedge of the active region 352 and can be exposed at a mesa on thepassivation layer 380 for a p-contact pad 382 to be deposited on thepassivation barrier layer 376. An n-contact 384 can be formed on then-type layer 360 in the active structure holes 378 and a conductiven-type layer vias 388 can be formed through the passivation layer 380and between the n-type contact 384 and an interconnecting metal layer386. An n-contact pad 400 is included in electrical contact with theinterconnecting metal layer 386, and in the embodiment shown is includedon a via plug that is on or in electrical contact with theinterconnecting metal layer 386. All of the above layers can be on aninsulation layer 396, with some LED chips according to the presentinvention also having some or all of the additional layers describedabove.

As mentioned above, the reflective and conducting characteristics orfunctions of the interconnection metal layer 386 are provided withdifferent layers or materials. In the embodiment shown, theinterconnecting metal layer 386 retains its conductivitycharacteristics, but can be made of a material that resistselectromigration. These materials can be less reflective and can absorbLED light emitting toward the interconnection metal layer 386. This canultimately result in reduced emission efficiency for the LED chip 600.To address this, additional layers or features can be included thatprovide the reflectivity characteristics or functions in areas where theinterconnecting metal layer 386 is exposed to light from the LED chip'sactive regions 352. This prevents the light reaching the interconnectingmetal layer where a portion of it can be absorbed, and also reflects thelight so it can contribute to use emission from the LED chip.

In different embodiments additional reflective layers can be included inmany different locations in the LED chip 600. In the embodiment shown athird reflective layer 602 can be included that is embedded in the LEDchip 600 in areas below the active regions 352 and above theinterconnection metal layer 386. In the embodiment shown, the thirdreflective layer 602 can be below the streets 604, and can be includedaround the outside edges of the active regions 352. These edge portionsof the third reflective layer 602 can be in the layers below the activeregions 352 and extending out from beyond the edges of the activeregions 352. At least a portion can be below and extending beyond thearea covered by the p-contact pad 382, with another portion of thesecond reflector layer 506 extending out from the edge of the n-contactpad 400.

The third reflective layer 602 can be in different locations in thelayer structure of the LED chip 600. In the embodiment shown the thirdreflective layer 602 can be embedded in the passivation layer 380 and iselectrically isolated from other layers of the LED chip 600. That is,the third reflective layer 602 does not carry electrical signals duringoperation of the LED chip 600, but are instead provided only for thereflective characteristics. The reflector layers are located in theareas where the less reflective interconnection metal layer 386 would bevisible or where LED light might otherwise be able to reach theinterconnection metal layer 386 where some of it may be absorbed.Portions of the third reflective layer 602 that are below the street 604reflect LED light that would otherwise continue on to theinterconnection metal layer 386 between the active regions 352. Portionsof the third reflective layer 602 around the edge of the active regions352 similarly reflect light that would otherwise reach theinterconnecting metal layer 386 beyond the edges of the active regions352.

The third reflective layer 602 can be made of many different reflectivematerials, with some embodiments comprising reflective metals such asAg, Au, Al or combinations thereof in mixture/alloy or in a stack ofdifferent layers of different materials. In some embodiments the thirdreflective layer can comprise Al or can comprise Al with an adhesionmaterial such as Ti with third reflective layer 602 comprising and Al/Tistack. The third reflective layer 602 can also be deposited using knownmethods, as described above. In other embodiments, the third reflectivelayer 602 can comprise non-metallic materials, such as dielectricmaterials that can be arranged as one or multiply layered reflectorssuch as distributed Bragg reflectors (DBRs).

When used in conjunction with the third reflective layer 602, theinterconnection metal layer 386 can comprise any of the many materialsdescribed above, either alone or in combination. In this embodiment,less reflective materials can be used that resist electromigration, withthe preferred materials comprising broad band reflectors. In someembodiments, the conductive interconnection metal layer 386 can comprisedifferent materials that can provide for good adhesion to surroundinglayers, barriers to surrounding layers and for conduction of anelectrical signal.

In some embodiments the interconnection metal layer 386 can comprise anadhesion and/or diffusion layers sandwiching a current conduction layer.These arrangements are particularly applicable to high current LED chipoperation with the interconnection metal layer 386 carry elevatedcurrent levels. The barrier and or adhesion layers can comprisematerials such as Ti, TiW and

Pt either alone or in combination. In some embodiments a stack of layerhaving different materials can serve as an adhesion/barrier layer withthe stack in one embodiment comprising alternating layers of materials.In some embodiments according to the present invention theadhesion/barrier stack can comprise TiW_Pt_TiW_Pt_TiW_Pt_TiW, etc., withthe underscore showing transition between layers. This stack cancomprise different number of Ti/W pairs and can have differentthicknesses. It is understood that in other embodiments this stack cancomprise other materials in different layer combinations.

The interconnection metal layer can also comprise different materialsfor the electrically conductive layer, such as Ni, Au, Ag and Cu, eitheralone or combination. It is also understood that the layers in differentembodiments can have different thicknesses. The following are differentembodiments of interconnection metal layers using an adhesion/barrierstack, with the adhesion/barrier stack being the topmost layers of theinterconnection metal layer:

-   Adhesion/Barrier Stack_4kAu_TiW-   Adhesion/Barrier Stack_4kNi_TiW-   Adhesion/Barrier Stack_4kPd_TiW

The 4 k refers to a thickness of approximately 4000 angstroms forconductive material, although other thicknesses can also be used such asless than 3000 angstroms or greater than 5000 angstroms. The TiW layeralso serves as a barrier layer against diffusion (conductive materialout or other materials in) and also serves as a current conductor,although it is a less efficient conductor than the electricallyconductive layer.

Other embodiments can also comprise interconnection metal layers withfewer or more layers, with some embodiments being provided without anadhesion/barrier stack. Instead, these embodiments can comprise only aconductive layer with barrier. One such embodiment can comprise Ni_TiW,with the Ni layer having different thicknesses such as approximately4000 angstroms, although other thicknesses can also be used.

It is understood that other embodiments of interconnection metal layerscan comprise different layers performing the same or similar functionsas described above, but may not include an adhesion/barrier stack. Theselayers can comprise a layer of material with some embodiments using Ti,Pt or TiW of different thickness with different electrically conductivelayers. Some embodiments of these layers can comprise Ti_Ni_TiW with theNi layer having thicknesses in the range of 50-500 angstroms or more. Itis understood that other interconnection metal layer embodiments cancomprise many different layers arranged in different ways. For example,one embodiment can comprise TiPdNi_4kAu_TiW.

FIGS. 27 and 28 show the electrical path through the LED chip 600 duringoperation, with the electrical signal following a path through theemitter that is similar to the LED chip 350 shown in FIG. 21 . Indifferent embodiments the active regions 352 can be arranged in manydifferent ways and as shown in FIG. 24 , they can be arranged linearly.In FIG. 28 , the active regions 352 are arranged in a square with anelectrical path 610 in FIGS. 27 and 28 showing current flowing betweenthe active regions 352, with active regions 352 being serially connectedsuch that the electrical signal conducts around the LED chip. This isonly one of the ways that current can flow through LED chips accordingto the present invention. Although only two and four active regions 352are shown in FIGS. 26 and 27 , respectively, it is understood that LEDchips according to the present invention can have many more activeregions, and in those embodiments, the signal then passes on to the nextof the active regions 352 connected in series and this continues untilthe last of the active regions 352. In different embodiments the activeregions can be coupled together in different series and parallelinterconnections.

During operation an electrical signal following a path through theactive regions as shown by arrows 404, with the portion of the pathbetween the active regions shown by path 610. In LED chip 600 theelectrical signal is applied to the p-contact pad 382 and is conductedthrough the barrier layer 376, metal layer 368, and current spreadinglayer 364, to the p-type layer 358. The signal then passes through tothe n-type layer 360 where it passes through to the n-contact 384 andthe n-type vias 388. The signal then conducts along the interconnectingconductive layer 386 where it passes into the first of the p-type vias398 and into the barrier layer for the next in line of the activeregions 352. The steps above are generally repeated for each of thesecond through until the last of the active regions 352. At the last ofthe active regions the signal is conducted to the p-type layer 358 inthe last active region 352, where it passes into the n-type layer 360,n-contact 384 and n-type vias 388. The signal is then conducted to then-contact pad 400. As mentioned above, the third reflective layer 602 iselectrically isolated from the other current carrying layers in the LEDchip 600, but in other embodiments the reflective layer 602 can be inelectrical contact with one or more layers and can be arranged to carrycurrent during operation.

It is understood that other LED chip embodiments according to thepresent invention can be provided with different arrangements to addresselectromigration, with some of the embodiments not having separatereflective layers. These embodiments can have arrangements to maintainthe reflectivity of the interconnection metal layer 386 while alsominimizing electromigration. Referring now to FIG. 29 , some embodimentscan comprise an interconnection metal layer 386 comprising alternatinglayers of different materials with different properties. In someembodiments, the interconnect layer can comprise a first layer 620 thatis an efficient electrical conductor but may be susceptible toelectromigration. In some embodiments, the first layer 620 can alsoefficiently reflect LED chip light. A second layer 622 can be includedthat is less reflective but has higher resistance to electromigrationthan the first layer. In some embodiments, the second layers can havereflective properties so that the interconnection metal layer isreflects LED chip light.

The interconnection metal layer 386 can comprise alternating first andsecond layers 620, 622 that can alternately exhibit the properties ofhigh reflectivity and resistance to electromigration. In differentembodiments, there can be different numbers of these alternating layerswith one embodiment comprising one or more conductive and highlyreflective layers sandwiched between layers that are resistant toelectromigration.

The multilayer arrangement can comprise any of the different materialsdescribed above including metals and dielectrics, or combinationsthereof. Some embodiments can comprise at least a first layer thatcomprises a metal such as an Au for efficient electrical conductivity.This first layer can be sandwiched between layers to resistelectromigration such as any of the materials discussed above, includingAl, Ti, TiW and Pt. Different embodiments can have a plurality ofalternating layers, with some embodiments having Al layers as thebottommost and topmost layers.

Still other conductive interconnect layer arrangements according to thepresent invention can be arranged differently to provide the desiredreflectivity with resistance to electromigration. In some embodiments,the conductive interconnect layer 386 can comprise a high reflectivitymaterial that includes an alloying materials to increase the resistanceto electromigration. Many of the above materials can be used in thelayer, with some embodiments comprising Al with various amounts ofalloying materials such as copper, silicon, scandium or other possiblealloying elements. The layer can be fabricated using known methodsdescribed above.

Although applicants do not wish to be bound by any one theory of howsuch alloyed layers function, it is believed that when certainreflective metal materials experience electromigration, the metalmaterial typically migrates along grain boundaries of the surroundingmaterial. It is also believed that the alloying materials tend to crowdthe grain boundaries, and that sometimes relatively small amounts ofalloying materials can be used. This crowding results in a “traffic jam”at the grain boundaries that effectively blocks some or all of theelectromigration of the reflective metal. The alloying material can beincluded in the conductive interconnect layer in differentconcentrations, with some embodiments having alloying materials in therange of 1-20%. In still other embodiments the concentration of alloyingmaterials can be in the range of 1-10%. In still other embodiments theconcentration of alloying material can be approximately 1-5%.

It is understood that the embodiments according to the present inventioncan be used with many different LEDs or LED chips having differentarchitecture and layer arrangements beyond those described above. Theembodiments above are discussed with structures where the growthsubstrate can be removed as part of the fabrication process, with theseembodiments having active structures mounted on a submount. Theinterconnecting layers are part of the LED chip and are primarily in thesubmount. In some of these embodiments, dielectrics can be used forisolating the current flow on both sides of the chip.

The present invention can also be used in LED chip embodiments where thegrowth substrate is not removed, with some of these embodiments having ashaped or textured substrate to enhance light extraction. One embodimentof LED chip according to the present invention can comprise anarchitecture similar to those commercially available from Cree Inc.,under its DA family of LED chips. The growth substrate can be made ofdifferent materials such as silicon carbide (SiC), sapphire, galliumnitride (GaN) or others. These types of chips are generally described inU.S. Pat. No. 8,368,100 to Donofrio et al., entitled “SemiconductorLight Emitting Diodes Having Reflective Structures and Methods ofFabricating Same,” which is incorporated herein by reference. The DAtype chip is not fabricated on a submount. Instead, the active region orregions are on a growth substrate and the chip is flipped over forattachment to a component that has interconnect features. In some ofthese embodiments the active region can be between the interconnectelement and the growth substrate. In some of these embodiments thegrowth substrate can be the primary emission surface and with the activeregion or regions between the substrate and component. Some of thesestructures can comprise entirely or partially oblique facets on one ormore surfaces of the chip.

Although the present invention has been described in detail withreference to certain preferred configurations thereof, other versionsare possible. Therefore, the spirit and scope of the invention shouldnot be limited to the versions described above.

What is claimed is:
 1. A monolithic LED chip, comprising: an LED chipstructure that is divided into a plurality of active regions;electrically conductive interconnect elements between active regions ofthe plurality of active regions; and first reflective elements that arearranged in passivation material, that are aligned with streets betweenadjacent active regions of the plurality of active regions, and that areelectrically isolated from the plurality of active regions.
 2. Themonolithic LED chip of claim 1, wherein the passivation materialcomprises SiO₂.
 3. The monolithic LED chip of claim 1, wherein thepassivation material comprises silicon nitride.
 4. The monolithic LEDchip of claim 1, wherein a distance between adjacent active regions ofthe plurality of active regions is no more than 15 microns.
 5. Themonolithic LED chip of claim 1, wherein a distance between adjacentactive regions of the plurality of active regions is no more than 10microns.
 6. The monolithic LED chip of claim 1, wherein a distancebetween adjacent active regions of the plurality of active regions is nomore than 5 microns.
 7. The monolithic LED chip of claim 1, wherein adistance between adjacent active regions of the plurality of activeregions is in a range from 0.05 microns to no more than 15 microns. 8.The monolithic LED chip of claim 1, wherein the electrically conductiveinterconnect elements are in electrical contact with the plurality ofactive regions on a same side of the plurality of active regions.
 9. Themonolithic LED chip of claim 1, wherein the first reflective elementscomprise a higher reflectivity than a reflectivity of the electricallyconductive interconnect elements.
 10. The monolithic LED chip of claim1, wherein the electrically conductive interconnect elements comprise amaterial that resists electromigration under high current operation. 11.The monolithic LED chip of claim 1, wherein the first reflectiveelements are arranged below said plurality of active regions, andarranged between the plurality of active regions and the electricallyconductive interconnect elements.
 12. The monolithic LED chip of claim1, further comprising second reflective elements that are arrangedaround an edge of one or more active regions of the plurality of activeregions.
 13. The monolithic LED chip of claim 12, wherein the first andsecond reflective elements comprise discontinuous portions of at leastone reflective layer.
 14. The monolithic LED chip of claim 1, whereinthe plurality of active regions comprise a growth substrate.
 15. Themonolithic LED chip of claim 14, wherein the growth substrate comprisessapphire.
 16. The monolithic LED chip of claim 14, wherein the growthsubstrate comprises silicon carbide.